The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the electronics industry utilized various methods and devices to protect circuits from voltage transients. In some applications, it was desirable to plug or unplug electronic circuits from their power source without removing the power. This may have occurred when a circuit card was inserted or removed from a small system such as a personal computer or from a large system such as a telecommunications system that may have a large rack full of electronic cards. Cards often were removed and re-inserted without powering down the entire system. These situations were referred to as “hot swap” or “hot plug” applications since the power lines remained “hot” during the transfers.
One example of a hot swap circuit for controlling the voltage applied to the power bus of a card during a hot swap event was disclosed in U.S. Pat. No. 6,781,502 that was issued to Stephen Robb on Aug. 24, 2004 which is hereby incorporated herein by reference. During hot swap events, it generally was desirable to slowly couple the input power to the power bus of the card that was being plugged in during the hot swap event. However, most hot swap controllers did not sufficiently limit the rise time of the voltage on the power bus of the card. Such rapid rise times caused disturbances on the power bus which could result in damaged components or a system crash.
Accordingly, it is desirable to have a hot swap control method and circuit that provides a long rise time for the voltage that is applied to the power bus of a card during a hot swap event.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of a MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay between the reaction that is initiated by the initial action.